.\" Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl), 24 September 1998
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\"     Added notes on capability requirements
.\"
.TH reboot 2 2024-05-02 "Linux man-pages 6.9.1"
.SH NAME
reboot \- reboot or enable/disable Ctrl-Alt-Del
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.RB "/* Since Linux 2.1.30 there are symbolic names " LINUX_REBOOT_*
   for the constants and a fourth argument to the call: */
.P
.BR "#include <linux/reboot.h>  " \
"/* Definition of " LINUX_REBOOT_* " constants */"
.BR "#include <sys/syscall.h>   " "/* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.P
.BI "int syscall(SYS_reboot, int " magic ", int " magic2 ", int " op ", void *" arg );
.P
/* Under glibc and most alternative libc's (including uclibc, dietlibc,
   musl and a few others), some of the constants involved have gotten
.RB "   symbolic names " RB_* ", and the library call is a 1-argument"
   wrapper around the system call: */
.P
.BR "#include <sys/reboot.h>    " "/* Definition of " RB_* " constants */"
.B #include <unistd.h>
.P
.BI "int reboot(int " op );
.fi
.SH DESCRIPTION
The
.BR reboot ()
call reboots the system, or enables/disables the reboot keystroke
(abbreviated CAD, since the default is Ctrl-Alt-Delete;
it can be changed using
.BR loadkeys (1)).
.P
This system call fails (with the error
.BR EINVAL )
unless
.I magic
equals
.B LINUX_REBOOT_MAGIC1
(that is, 0xfee1dead) and
.I magic2
equals
.B LINUX_REBOOT_MAGIC2
(that is, 0x28121969).
However, since Linux 2.1.17 also
.B LINUX_REBOOT_MAGIC2A
(that is, 0x05121996)
and since Linux 2.1.97 also
.B LINUX_REBOOT_MAGIC2B
(that is, 0x16041998)
and since Linux 2.5.71 also
.B LINUX_REBOOT_MAGIC2C
(that is, 0x20112000)
are permitted as values for
.IR magic2 .
(The hexadecimal values of these constants are meaningful.)
.P
The
.I op
argument can have the following values:
.TP
.B LINUX_REBOOT_CMD_CAD_OFF
.RB ( RB_DISABLE_CAD ,
0).
CAD is disabled.
This means that the CAD keystroke will cause a
.B SIGINT
signal to be
sent to init (process 1), whereupon this process may decide upon a
proper action (maybe: kill all processes, sync, reboot).
.TP
.B LINUX_REBOOT_CMD_CAD_ON
.RB ( RB_ENABLE_CAD ,
0x89abcdef).
CAD is enabled.
This means that the CAD keystroke will immediately cause
the action associated with
.BR LINUX_REBOOT_CMD_RESTART .
.TP
.B LINUX_REBOOT_CMD_HALT
.RB ( RB_HALT_SYSTEM ,
0xcdef0123; since Linux 1.1.76).
The message "System halted." is printed, and the system is halted.
Control is given to the ROM monitor, if there is one.
If not preceded by a
.BR sync (2),
data will be lost.
.TP
.B LINUX_REBOOT_CMD_KEXEC
.RB ( RB_KEXEC ,
0x45584543, since Linux 2.6.13).
Execute a kernel that has been loaded earlier with
.BR kexec_load (2).
This option is available only if the kernel was configured with
.BR CONFIG_KEXEC .
.TP
.B LINUX_REBOOT_CMD_POWER_OFF
.RB ( RB_POWER_OFF ,
0x4321fedc; since Linux 2.1.30).
The message "Power down." is printed, the system is stopped,
and all power is removed from the system, if possible.
If not preceded by a
.BR sync (2),
data will be lost.
.TP
.B LINUX_REBOOT_CMD_RESTART
.RB ( RB_AUTOBOOT ,
0x1234567).
The message "Restarting system." is printed, and a default
restart is performed immediately.
If not preceded by a
.BR sync (2),
data will be lost.
.TP
.B LINUX_REBOOT_CMD_RESTART2
(0xa1b2c3d4; since Linux 2.1.30).
The message "Restarting system with command \[aq]%s\[aq]" is printed,
and a restart (using the command string given in
.IR arg )
is performed immediately.
If not preceded by a
.BR sync (2),
data will be lost.
.TP
.B LINUX_REBOOT_CMD_SW_SUSPEND
.RB ( RB_SW_SUSPEND ,
0xd000fce1; since Linux 2.5.18).
The system is suspended (hibernated) to disk.
This option is available only if the kernel was configured with
.BR CONFIG_HIBERNATION .
.P
Only the superuser may call
.BR reboot ().
.P
The precise effect of the above actions depends on the architecture.
For the i386 architecture, the additional argument does not do
anything at present (2.1.122), but the type of reboot can be
determined by kernel command-line arguments ("reboot=...") to be
either warm or cold, and either hard or through the BIOS.
.\"
.SS Behavior inside PID namespaces
.\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
.\" see also commit 923c7538236564c46ee80c253a416705321f13e3
Since Linux 3.4,
if
.BR reboot ()
is called
from a PID namespace other than the initial PID namespace
with one of the
.I op
values listed below,
it performs a "reboot" of that namespace:
the "init" process of the PID namespace is immediately terminated,
with the effects described in
.BR pid_namespaces (7).
.P
The values that can be supplied in
.I op
when calling
.BR reboot ()
in this case are as follows:
.TP
.B LINUX_REBOOT_CMD_RESTART
.TQ
.B LINUX_REBOOT_CMD_RESTART2
The "init" process is terminated,
and
.BR wait (2)
in the parent process reports that the child was killed with a
.B SIGHUP
signal.
.TP
.B LINUX_REBOOT_CMD_POWER_OFF
.TQ
.B LINUX_REBOOT_CMD_HALT
The "init" process is terminated,
and
.BR wait (2)
in the parent process reports that the child was killed with a
.B SIGINT
signal.
.P
For the other
.I op
values,
.BR reboot ()
returns \-1 and
.I errno
is set to
.BR EINVAL .
.SH RETURN VALUE
For the values of
.I op
that stop or restart the system,
a successful call to
.BR reboot ()
does not return.
For the other
.I op
values, zero is returned on success.
In all cases, \-1 is returned on failure, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EFAULT
Problem with getting user-space data under
.BR LINUX_REBOOT_CMD_RESTART2 .
.TP
.B EINVAL
Bad magic numbers or
.IR op .
.TP
.B EPERM
The calling process has insufficient privilege to call
.BR reboot ();
the caller must have the
.B CAP_SYS_BOOT
inside its user namespace.
.SH STANDARDS
Linux.
.SH SEE ALSO
.BR systemctl (1),
.BR systemd (1),
.BR kexec_load (2),
.BR sync (2),
.BR bootparam (7),
.BR capabilities (7),
.BR ctrlaltdel (8),
.BR halt (8),
.BR shutdown (8)
